1. Field of the Invention
The present invention relates to signal processing, and, in particular, to the compensation of frequency offsets in decoding received signals.
2. Description of the Related Art
In certain modulation schemes, such as multi-phase shift keying, frequency offsets between the carrier frequency of a received signal and the local oscillator frequency of the receiver can inhibit the ability of the receiver to accurately decode the information contained in the received signal. For example, in a cordless telephone communication system, there may be a frequency offset between the signal received by a cordless phone from a base station and the frequency of the local oscillator in the cordless phone handset.
If the telephone equipment is designed with expensive crystal oscillators, the frequency offset between the carrier and the local oscillator can be kept to within a few percentage points of the baud rate. For example, in a communication system having a baud rate of 100 kbaud/sec, expensive crystal oscillators can be used keep the frequency offset to within about 1 kHz.
Unfortunately, using expensive crystal oscillators adds significantly to the cost of the cordless phone equipment. Using less expensive oscillators would keep phone equipment costs down, but would result in larger frequency offsets. For example, in a relatively inexpensive system having a baud rate of 100 kbaud/sec, frequency offsets could be as large as .+-.20 kHz, implying a frequency offset range of up to 40% of the baud rate.